Bryan Hanson, PhD
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 An example of one of the vascular-protective flavonoids is quercetin, which is also found in numerous other plants (see Figure 4.21). The chief structural difference between flavonoids and anthocyanidins (and anthocyanins) is that in the latter, the oxygen in the middle ring bears a positive charge. The medicinal activity of the anthocyanidins and anthocyanins appears to be similar to the flavonoids. Cyanin is one of the blue pigments found in blueberries (Vaccinium myrtillus). Delphinidin, discussed in Chapter 3, is another example of an anthocyanidin (see Figure 3.11). |
Earl Mindell, R.Ph., Ph.D.
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 In addition, quercetin can block the release of even stronger inflammatory agents, leukotrienes, which are involved in asthma, psoriasis, gout, ulcerative colitis, and other common ailments. Although everyone can benefit from quercetin, people with allergies and inflammatory conditions should be vigilant about getting enough of this bioflavonoid. If you don't eat an onion or two daily, take quercetin supplements.
Possible Benefits
Strengthens capillaries, promotes good circulation. Is a powerful anticancer compound. Is a natural anti-inflammatory agent. Can relieve allergic symptoms. |
Henry Pasternak, D.V.M., C.V.A.
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 Quercetin inhibits the inflammation-producing enzyme (cyclooxygenase) and its subsequent inflammatory mediators (leukotriens and prostaglandins).26,27 quercetin also stabilizes mast cells and basophils.28
Quercetin in clinical practice does possess some anti-inflammatory and anti-histaminic effects; however, its effects may not be realized for several weeks. Though dogs and cats produce vitamin C, under times of disease and stress, it is important to provide it in the diet. I am not referring to ascorbic acid, which has no healing ability, but to fruits and vegetables. |
| Unfortunately, when used as isolated nutrients, they must be used with enzymes to enhance absorption. quercetin inhibits the inflammation-producing enzyme (cyclooxygenase) and its subsequent inflammatory mediators (leukotriens and prostaglandins).26,27 quercetin also stabilizes mast cells and basophils.28
Quercetin in clinical practice does possess some anti-inflammatory and anti-histaminic effects; however, its effects may not be realized for several weeks. Though dogs and cats produce vitamin C, under times of disease and stress, it is important to provide it in the diet. |
Amarjit S. Basra
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 In another test, pairs of flavonoids taken from genistein, baicalein, hesperetin, naringenin, and quercetin were shown to be synergistic in inhibition of a human breast cancer cell line.
It is evident that this isobol method cannot be applied to herbal extracts or extract mixtures. Here detailed pharmacological investigations with single constituents or mixtures of them in comparison to an extract fraction or the whole extract must be used. In Table 1.1 are listed those herbal drugs for which pharmacological evidence of this potentiated synergistic effects has been assessed. |
Russell L. Blaylock, M.D.
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 Interestingly, the flavonoid, quercetin, is also very protective.
As we age a certain enzyme, called MAO-B, increases in our brain, and this enzyme can increase brain damage by producing harmful compounds. In Parkinson's disease, one of the more effective drugs works by inhibiting this enzyme. Ginkgo biloba extract also inhibits MAO-B, as do several other flavonoids.485 It has been proposed that by inhibiting this enzyme, Ginkgo acts to relieve stress and promote a sense of calm. |
Amarjit S. Basra
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| In fact, tea may very well be the major source of antioxidant worldwide, due to the very high concentration of these compounds—for example, quercetin, kaempferol, myrecitin, and epigallocatechin gallate—in tea, combined with the frequent consumption of this beverage. Tea is second to water as the most widely consumed beverage worldwide.
Several in vitro studies have shown the potent antioxidant activities of tea extracts, which also possess interesting tumor-inhibiting properties. |
Byron J. Richards, CCN
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 There is data to support the use of quercetin and Tamoxifen together, helping to synergistically make cancer more susceptible to medical treatment.835
Indole-3-caribinol (I3C) is the active component of cruciferous vegetables, mentioned in the chapter on prostate cancer. Several studies conducted in the early 1990s demonstrated that 400 mg of 13 C per day in women can normalize the way estrogen is metabolized so that it will not go down a pathway that could stimulate cancer. |
Russell L. Blaylock, M.D.
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| This may explain, in part, how flavonoids protect against cancer and other degenerative diseases, especially heart attack and strokes. quercetin, rutin, hesperidin, and curcumin are especially powerful iron-chelating flavonoids, and all can be purchased from health food stores and suppliers.
It is important to note that Vitamin C can actually overcome the blocking effect of flavonoids by dramatically increasing iron absorption, and the amount that will increase absorption is quite small. For this reason, I advise taking vitamin C on an empty stomach. |
| Curcumin, quercetin, and apigenin (also in celery) all inhibit the enzyme protein kinase-C, that causes much of the microvascular damage associated with diabetes.
Finally, a series of studies has shown that diabetic patients have significantly elevated homocysteine levels, and that at the same time, they developed kidney damage.404 As we have seen, elevated homocysteine levels are associated with rapid and extensive atherosclerosis. The studies found that diabetics with the earliest age of onset and poorest metabolic control had the highest homocysteine levels. |
| Green tea contains high levels of the powerful antioxidant, quercetin, as well as special flavonoids, including epicatechin and epigallocatechin 3-gallate. These flavonoids not only reduce oxidation of LDL cholesterol, but have powerful anticancer effects as well.1'6
In one interesting study, calcification of the aorta, as seen on x-ray, was used to follow progression of atherosclerosis in a group of men and postmenopausal women. |
| Mix with one tablespoon extra virgin olive oil or Omega-3 oil. quercetin 250 mg
Dissolve in oil or take a water-soluble form, twice a day
Milk Thistle 200 mg
Take two capsules twice a day.
DHEA
25-50 mg a day under medical supervision only.
Vinpocetine 10 mg
Take one twice a day.
B-100 multivitamin with minerals and no iron
Take one a day.
The human immune system is a highly complex, bodywide network of specialized cells, organs, and even a separate circulatory system, which work in concert to clear infection from the body. The organs of the immune system are called lymphoid organs. |
Amarjit S. Basra
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| Measurement of trans-resveratrol, (-t-)-catechin, and quercetin in rat and human blood and urine by gas chromatography with mass selective detection, Methods Enzymol, 335: 130-145; Scalbert, A. and Williamson, G., 2000, Dietary intake and bioavailability of polyphenols, J. Nutn, 130: 2073-2085; Kuhnle et al., 2000, Resveratrol is absorbed in the small intesting as resveratrol glucoronide.
46. Tikkanen et al., 1998, Effect of soybean phytoestrogen intake on low density lipoprotein; Halliwell, Zhao, and Whiteman, 2000, The gastrointestinal tract.
47. Malins, D.C., Hellstrom, K.E., Anderson, K. |
Joseph E. Mario
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 A n
•BIOFLAVONOIDS Complex comprises at least 20,000 organic compounds of Carbon, Oxygen and Hydrogen; also known as Vitamin P for capillary Permeability (with Hesperidin, quercetin, Rutin, and Tangeretin), and Vitamin C2. There are four groups of Flavonoids - brightly-colored Flavanones, Flavonals, Flavones and Chalcones; including violet, red or blue Anthocyanosides, and Proanthocyanidins (in Grape seeds and Pine bark) which are found associated with Vitamin C for antioxidant protection in plants against wind, rain, temperature, and ultraviolet sunlight. |
Russell L. Blaylock, M.D.
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| I recommend:
Vitamin C (buffered): 500 mg three times a day on an empty stomach Quercetin: 500 mg three times a day
Vitamin E succinate or natural form vitamin E. 400 IU twice a day
Niacinamide: 500 mg daily
Folate: 800 ug a day
Methylcobalamin: 1,000 ug a day
N-acetyl-L-cysteine: 750 mg a day
Alpha-lipoic acid: 200 mg twice a day
Selenium: 200 ug a day
Start these supplements at least three weeks before x-rays are taken. |
Michael T. Murray
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 The most commonly used flavonoid supplements are citrus bioflavonoids (including rutin and hesperidin), quercetin, grapeseed and pine bark extracts, and green tea extracts. For prevention of diabetes we would list these flavonoids in the opposite order. Citrus bioflavonoids are the most widely used and least expensive flavonoid sources. However, they are also the least active. One of the most beneficial groups of flavonoids is the proanthocyanidins (also referred to as procyanidins). These molecules are found in high concentrations (up to 95 percent) in grapeseed and pine bark extracts. |
Alan R. Gaby, M.D., Jonathan V. Wright, M.D., Forrest Batz, Pharm.D. Rick Chester, RPh., N.D., DipLAc. George Constantine, R.Ph., Ph.D. Linnea D. Thompson, Pharm.D., N.D.
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 Active constituents
Two sets of compounds make up the majority of onion's known active constituents—sulfur compounds, such as allyl propyl disulphide (APDS), and flavonoids (page 516), such as quercetin (page 580). Each of these groups of compounds has multiple medicinal actions. The sulfur compounds form a strongly scented oil, particularly the compound known as thioproanal-s-oxide or lacrimatory factor. It is responsible for the tearing many people suffer while cutting onions.5 Onion and onion oil constituents have been repeatedly shown to kill various microbes in the test tube.6 |
Richard Beliveau, Ph.D. and Denis Gingras, Ph.D.
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 Even more interesting from a nutritional point of view are recent results indicating that certain molecules of dietary origin, including quercetin and especially resveratrol, are very powerful sirtuin activators; it is this activation that may increase cell longevity. For example, the addition of resveratrol to a growth culture of single-celled organisms such as yeast increases cell lifespan by 80%. Generally, yeasts live for nineteen generations; adding resveratrol boosted life expectancy to a maximum of thirty-eight generations! |
| Nevertheless, in the case of onions, the important contribution of other classes of molecules should not be overlooked: polyphenols such as quercetin, for example, a molecule able to prevent the growth of a great number of lab-grown cancer cells and which interferes with the development of cancers in animals. In any case, with respect to the most current research findings, it is more and more certain that the compounds found in garlic and onions may act as powerful inhibitors of cancer growth by targeting at least two processes involved in tumour formation. |
| From a phytochemical point of view, the onion is a major source of the flavonoid quercetin, containing up to 50 mg per one hundred grams. The molecule responsible for the onion's lachrymal properties, propanethial S-oxide, is released by breaking or tearing the bulb, but since this substance is very soluble in water, it can easily be eliminated by rinsing the peeled bulb under running water.
Leeks
Of a more subtle flavour than its cousins, the leek (Allium porrum) is originally from the Mediterranean region, or more probably the Middle East. |
Michael Friedman, ND
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 Of the naturally occurring flavonoids, luteolin was the most active inhibitor of 5'-deiodinase activity when tested in vitro; however, quercetin, myricetin, and flavonoids with chalcone, aurone and flavone structures have also been shown to have in vitro inhibitory activity.2,137
It is not known whether similar effects occur in vivo or whether, if such effects do occur, they are restricted to specific flavonoid compounds or dosages. |
Alan R. Gaby, M.D., Jonathan V. Wright, M.D., Forrest Batz, Pharm.D. Rick Chester, RPh., N.D., DipLAc. George Constantine, R.Ph., Ph.D. Linnea D. Thompson, Pharm.D., N.D.
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| Some doctors are currently experimenting with 400 to 1,000 mg of quercetin three times per day.
Bromelain (page 481) reduces the thickness of mucus, which may be beneficial for those with asthma,68 though clinical actions in asthmatics remain unproven.
Some researchers have suggested that asthma attacks triggered by exercise might be caused by free-radical damage caused by the exercise. Beta-carotene (page 469) is an antioxidant (page 467) that protects against free-radical damage. |
J. Robert Hatherill
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 More than 135 slightly different quercetin compounds exist, such as rutin, which is used to treat fragile capillaries (tiny blood vessels). quercetin is the most abundant flavonol in red wine, where rutin is also present. As a rule the deeply red Cabernet Sauvignon has the highest quercetin content. Other dietary sources include broccoli, red grapes, shallots, and yellow squash.
Anticancer Benefits of the Onion Group
A number of qualities recommend the foods in this group. |
Michael T. Murray
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| In addition to controlling blood sugar levels, vitamin C, flavonoids such as quercetin, grapeseed extract, and bilberry extract can help lower intracellular sorbitol levels.
Increased Oxidative Damage
Increased oxidative stress is a major factor in the risk of the chronic complications of diabetes. As previously stated, individuals with diabetes typically have elevated levels of free radicals and oxidative compounds.3 These highly reactive compounds bind to and destroy cellular compounds. |
| Flavonoids such as quercetin promote insulin secretion and are potent inhibitors of glycosylation and sorbitol accumulation, while flavonoid-rich extracts such as bilberry and hawthorn extracts have been shown to be helpful in diabetic retinopathy and microvascular abnormalities.19
The beneficial effects of flavonoids in battling the complications of diabetes are numerous, including the fact that as antioxidants, flavonoids are generally more potent and effective against a broader range of oxidants than the traditional antioxidant nutrients vitamins C and E, beta-carotene, selenium, and zinc. |
Michael Janson, M.D.
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 Another effect of quercetin is to reduce the damage induced by tobacco smoke in the airway membranes. Even if you do not smoke yourself, it is hard to completely avoid exposure to secondhand smoke.
I usually suggest doses of 400 mg of quercetin twice per day for allergic patients and those at risk of cataract. Often, they need to increase the dose to 1200 or 1600 mg per day for asthma or nonresponsive allergy symptoms. The product I use contains 400 mg of quercetin, mixed with the enzyme bromelain to help enhance its absorption. |
Eric R. Braverman
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 Blood-flow enhancers such as quercetin and D, L-phenylalanine and herbs such as huperzine-A, Rhodiola rosea, and ginkgo have improved memory and focus in Alzheimer's patients. Supplements such as Cognitex, ProCog, and my Brain Youth and Brain Memory formulas are also vital to memory and cognitive functions. |
Patrick Holford
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 Because of this, the many benefits of quercetin include alleviating bruising, edema, varicose veins, and fragile capillaries.
A major benefit of quercetin is its ability to inhibit the release of histamine. It is said to help mitigate conditions brought on by some types of allergen (for example, eczema, asthma, hay fever) and has been ascribed anti-inflammatory properties, which means that berries could be good for arthritis sufferers as well. |
Gary Null, Ph.D.
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 Quercetin
Several studies have documented the anticancer activity of the bioflavonoid quercetin in vitro, while results from animal trials demonstrate cardioprotective and antidiabetic effects as well. Intravenous administration of quercetin and tocopherol acetate for seven days has been found to enhance normalization of clinical indices and restoration of the immune homeostasis in patients suffering from Flexner's dysentery. |
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